There was a waiting time, and the children used it to practice with their shells, using the thick stems of seaweed—thick as a man’s arm—to represent the ankles of the invading force, and they were soon fairly expert at the trick which was their duty. Francis had just nipped an extra fat stalk and released it again by touching the secret spring when the word went around, “Every man to his post!” The children proudly took up their post next to the Princess, and hardly had they done so when a faint yet growing sound knocked gently at their ears. It grew and grew and grew till it seemed to shake the ground on which they stood, and the Princess murmured, “It is the tramp of the army of the Under Folk. Now, be ready. We shall lurk among these rocks. Hold your good oyster shell in readiness, and when you see a foot near you clip it, and at the same time set down the base of the shell on the rock. The trusty shell will do the rest.” “Yes, we know, thank you, dear Princess,” said Mavis. “Didn’t you see us practicing?” But the Princess was not listening; she had enough to do to find cover for her troops among the limpet-studded rocks. And now the tramp, tramp, tramp of the great army sounded nearer and more near, and through the dimly lighted water the children could see the great Deep Sea People advancing. Very terrible they were, big beyond man-size, more stalwart and more finely knit than the Forlorn Hopers who had led the attack so happily and gloriously frustrated by the Crabs, the Narwhals and the Sea Urchins. As the advance guard drew near all the children stared, from their places of concealment, at the faces of these terrible foes of the happy Merland. Very strong the faces were, and, surprisingly, very, very sad. They looked—Francis at least was able to see it—like strong folk suffering proudly an almost intolerable injury—bearing, bravely, an almost intolerable pain. “But I’m on the other side,” he told himself, to check a sudden rising in his heart of—well, if it was not sympathy, what was it? And now the head of the advancing column was level with the Princess. True to the old tradition which bids a commander lead and not to follow his troops, she was the first to dart out and fix a shell to the heel of the left-rank man. The children were next. Their practice bore its fruit. There was no blunder, no mistake. Each oyster shell clipped sharp and clean the attached ankle of an enemy; each oyster shell at the same moment attached itself firmly to the rock, thus clinging to his base in the most thorough and military way. A spring of joy and triumph welled up in the children’s hearts. How easy it was to get the better of these foolish Deep Sea Folk. A faint, kindly contempt floated into the children’s minds for the Mer-people, who so dreaded and hated these stupid giants. Why, there were fifty or sixty of them tied by the leg already! It was as easy as—